/**
*      author: Y_Yao
*      created: 2025-02-08 20:02:21
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
const int N = 1000 + 7;
int n,m;

void solve()
{
    cin >> n >> m;
    unordered_set<int> s;
    for(int i = 1;i <= m;i++)
    {
        int x;
        cin >> x;
        s.insert(x);
    }
    cout << n - s.size() << endl;
    for(int i= 1;i <= n;i++)
    {
        if(s.count(i)) continue;
        cout << i << " ";
    }
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}